Process for producing grinding materials



United States Patent PROCESS FOR PRODUCING GRINDING ,MATERIALS TomohiroI-Iorle, Kyoto City, Japan No Drawing. Original application August 10,1953, Serial No. 373,458. Divided and this application March 20, 1957,Serial No. 651,125

2 Claims. (Cl. 51-296) This invention relates to a process for producinggrinding materials, and products thereby.

This application is a division of my prior U. S. application, Serial No.373,458, filed August 10, 1953, now abandoned, for Process for ProducingGrinding Materials and Products Thereby. 7

Generally speaking, this invention relates to a new type of grindingmaterials composed of a polyvinyl acetal bond of a texture which hasindependent pores connected acid, which may be added at any'appropriatetime prior to the acetal reaction beginning.

The grinding material according to this invention is composed of aspongy polyvinyl acetal bond, in which the pores are independent fromeach other but are connected with each other through fine capillarytubes, and having abrasive powders or particles distributed and retainedevenly among the pores throughout the bond.

The texture of the bond, even distribution of abrasives and thesubstance constituting the bond combined together give an excellentgrinding material which is especially adapted for performing theso-called superfinish operation.

The polyvinyl alcohol subjected to acetal reaction with formaldehydeunder a catalyst has been found to be most suitable for forming a bondfor holding abrasives, because the polyvinyl acetal offers, of itself, agrinding action due to its desirable elasticity, durability andhardness, while possessing a most desirable cohesive force for holdingabrasives most properly.

According to this invention, a polyvinyl acetal bond having a texturepossessing independent pores connected with each other through finecapillary tubes must be produced. In order to produce such a bond, ithas been found that a most uniformly foamed mass of polyvinyl alcoholmust be achieved. For this purpose, it has been previously suggestedthat an aqueous solution of polyvinyl alcohol be treated with a surfaceactive foaming agent. This agent is added directly to an aqueoussolution of polyvinyl alcohol, and subjected to stirring or agitation togive rise to a foamed mass having independent bubbles.

However, I have discovered that a most independent foamed mass ofpolyvinyl alcohol having independent bubbles can be produced, mosteasily and effectively, if a foamed mass of water, prepared separatelyby mixing 2,876,085 Patented Mar. 3, 1959 water with a surface activefoaming agent, is into an aqueous solution of polyvinyl alcohol. This isbelieved to be due to the fact that the foamed mass of water holds itsbubbles as they are, in an independent state, as the foamed mass isdispersed into the aqueous solution of polyvinyl alcohol-a surprisingphenomena that has been discovered. Instead, the most difiicult problemof producing a most uniformly foamed mass of polyvinyl alcohol has thusbeen solved according to the invention by mixing the foamed mass ofwater into an aqueous solution of polyvinyl alcohol.

Further, according to this invention, the problem of distributingabrasives most evenly throughout the bond has been solved by forming afoamed mass of polyvinyl alcohol having independent bubbles, completelyseparated from each other, and by suspending abrasives among the bubblesevenly and uniformly. This even and uniform distribution of abrasiveshas been heretofore a problem awaiting solution, and has been solved bythe invention.

According to this invention, a foamed mass of polyvinyl alcohol isprepared as follows:

Water is mixed with a surface active foaming agent, and the mixture issubjected to a suitable mechanical stirring or agitation so as to form afoamed mass of water having independent bubbles, and then the foamedmass of water is mixed into an aqueous solution of polyvinyl alcohol,and the whole mixture is subjected to a suitable mechanical stirring oragitation so as to form a foamed mass having independent bubbles.

As surface active foaming agents may be used egg albumen, protein,gelatine, saponin or the like foaming substance, possessing a most greatstability of holding up bubbles for a prolonged time.

As abrasives may be used diamond powder, silica sand, synthetic preciousstone powder, or other known abrasive powders of any kind in common use.

The acetal reaction may be carried out, as is well known, in thepresence of a catalyst such as hydrochloric or sulphuric acid, at roomor a higher temperature.

Abrasive powders may be added at any appropriate times prior to thebeginning of acetal action. It has been found most desirable to add theabrasive to the aqueous solution of polyvinyl alcohol prior to its beingmixed with the foamed mass of water.

The preferred method of practice has been found to consist in mixing afoamed mass of water with an aqueous solution of polyvinyl alcohol, thepolyvinyl alcohol solution having abrasives suspended therein. Acatalyst, for example, hydrochloric acid, and formaldehyde are added tothe mixture to indicate the acetal reaction. This mixture, viz., anacetal-reactant mixture, may, for example, be introduced into a mouldvessel, and left standing at room temperature, or heated to a highertemperature, to obtain a hardened mass which may be taken out of thevessel and dried, after water-washing, to give a grinding material whichmay be in the form of block, wheel, stick or any other appropriate form.

The acetal-reactant mixture can be applied to a suitable base material,such as cloth, to give a buff stick as the product.

Further, it is evidently within the scope of this invention to introduceor incorporate into the polyvinyl acetal a thermohardening syntheticresin, such as phenolor urea-formaldehyde resin, to modify thethermoplastic property of the latter. The product obtained in this wayhas been found especially suited to be used for grinding and cuttingpurposes. Alternatively, the thermo hardening resin may be impregnatedwithin into the pores of the spongy product of the invention by treatingthe latter with a solution of the resin. It is evident that theimpregnation should be controlled so as to retain the desired porosityof the spongy product. Instead of the thermo hardening synthetic resin,any kind of appropriate synthetic resin, or a suitable high molecularpolymerization product, or even Portland cement, or gypsum, or any otherappropriate inorganic substance may also be used for impregnating in asimilar manner the pores of the spongy product of this invention.

Other appropriate modifications by which this invention may be carriedout without departing from the spirit of the invention will be readilyapparent to those skilled in the art. The invention now will beillustrated and explained by reference to the practical examplesmentioned below:

Example 1 50 grs. polyvinyl alcohol in the form of a white powder wereadded to 310 cc. water and 80 cc. hydrochloric acid of specific gravityof 1.20, and the mixture was heated for 15 minutes at a temperature of80 C., and thereafter cooled, to obtain an aqueous solution of polyvinylalcohol. Separately, 100 grs. egg albumen was added to 100 cc. water andthe mixture was stirred mechanically to obtain a foamed mass of water.The foamed mass was then added to the aqueous solution of polyvinylalcohol prepared as above, and mixed uniformly, resulting in a uniformlyfoamed mass of polyvinyl alcohol, having an apparent volume of 300 cc.,in which the bubbles were distinct independent from each other. To thisfoamed mass was then added powdery silica sand of 1200 mesh size in aquantity equal to one-tenth the apparent volume of the foamed mass. Thefoamed mass was stirred in order to suspend the silica sand uniformlythroughout the foamed mass, and thereafter 100 cc. of 40% formalin wasadded, and the whole mass was again stirred. The mass was then pouredinto a cylindrical glass vessel of 90 mm. inner dia. and 3 mm. height,and left to stand at 25 C. for an hour, to harden the mass. The mass wasthen taken out of the vessel and dried and it was found to be a spongymaterial. The material was then cut into pieces of 5 mm. thickness, andimmersed in water to be softened, and after a suitable removal of watercontent, a product was obtained, containing an appropriate amount ofwater. This product was suitable for use as a grinding material foroptical glasses.

Example 2 20 grs. polyvinyl alcohol was added to 110 cc. water.

and grs. urea-formaldehyde resin, and this mixture was heated so as toproduce a solution. Thereafter, 270 grs. silicon carbide grain of 100mesh was added to the solution so as to obtain a sludge. Separately, 10cc. methyl cellulose solution was mixed with 20 cc. saponin solution of1% concentration and 70 cc. water, and air was blown into the mixture soas to produce a foamed mass of water, having three times volume comparedto the original quantity of water. The said foamed mass of water wasmixed with the sludge prepared as above, and stirred so as to produce afoamed mass, to which 45 cc. hydrochloric acid, 45 cc. formaldehyde and30 cc. methyl alcohol were added to obtain a foamed muddy mass. Thismass was then poured into a mould, and kept at a temperature of 40 C.,for 10-15 minutes, thereby bringing acetal reaction to completion. Then,the moulded mass was taken out of the mould and dried, afterwater-washing, to obtain a manufacture, viz., a synthetic grindingstone.

Example 3 40 cc. of 3% methyl cellulose solution was mixed with 10 cc.of 0.1% saponin solution, and a foamed mass was produced by stirring themixture as air was blown thereinto. Separately, 20% polyvinyl alcoholwas added to cc. water, and heated to obtain a solution, to which grs.of silicon carbide grains of 240 mesh were added. The resulting mixturewas mixed with the foamed mass produced as above, and the whole mass Wasstirred thoroughly, and thereafter, 30 cc. concentrated hydrochloricacid and 35 cc. formaldehyde were added and then the resulting mixturewas stirred to produce a uniform sludge. Said sludge was poured over aVinyon cloth in a thickness of 23 mm., and thereafter dried at atemperature of 40 C., for 12 hours, to bring acetal reaction tocompletion. Thereafter, the

product was-rinsed with water, and after drying, given a spray of lightoil, and then cut into pieces of a definite size. A plurality of suchpieces were superimposed and adhered together to form a bufi stonesuitable for grinding.

Example 4 The grinding material obtained by the process of Example 1, of18 mm. height, 30 mm. width and 15 mm. thickness, was impregnated with asolution of melamine resin dissolved in a paint thinner, and dried toobtain a product, viz., a grinding stone.

Example 5 A spongy sheet-like product of an annular form, obtained bythe process of Example 1, was impregnated with a solution of 80 grs.phenol-formaldehyde resin dissolved in 20 grs. methanol in a ratio of40%, and then, after drying at 40 C., pressed under hydrostaticpressure, so as to obtain a cutting blade of 0.3 mm. thickness,strengthened and possessing a highly promoted capacity. It was foundthat the blade was stronger and had a higher cutting capacity thansimilar non-impregnated blades.

in a similar manner, acryl type synthetic resins, or other types ofsynthetic resins may also be applied so as to obtain a similaradvantageous effect.

I claim:

1. A process for producing a cellular abrasive article having abrasiveparticles uniformly distributed therewithin, which comprises: forming anaqueous solution of polyvinyl alcohol; separately forming a stable,aqueous, foamed mass by mixing water with a surface active foaming agentand agitating same to form a stable foam having independent pores;mixing said foamed mass, abrasive particles and said aqueous solution ofpolyvinyl alcohol to form a uniformly foamed, aqueous, polyvinyl alcoholmass having abrasive particles uniformly distributed throughout;incorporating a catalyst in said foamed, aqueous, polyvinyl alcoholmass, and thereafter adding and uniformly mixing formaldehyde in saidfoamed, aqueous, polyvinyl alcohol mass to react the formaldehyde withthe polyvinyl alcohol to cause gelation and rigidification of said massand thereby produce a cellular article having independent pores interconnected by fine capillary tubes and having abrasive particlesuniformly distributed and retained in the gelled mass.

2. A process for producing a cellular abrasive article having abrasiveparticles uniformly distributed therewithin, which comprises: forming anaqueous solution of polyvinyl alcohol and tion reaction andincorporating abrasive particles therein; separately forming a stable,aqueous foamed mass by mixing water with a surface active foaming agentand agitating same to form a stable foam having independent pores;mixing said foamed mass and said aqueous solution containing abrasiveparticles to form a uniformly foamed, aqueous, polyvinyl alcohol masshaving abrasive particles uniformly distributed throughout; thereafteradding formaldehyde to said foamed aqueous polyvinyl aicohol mass anduniformlymixing same therein to cause an acid catalyst for a formalizaareaction between the formaldehyde and the polyvinyl mm Cited in the tileof this patent alcohol and thereby cause gelation'and rigidification ofUNITED STATES PATENTS said mass to produce a cellular article havingindependent 2 609 347 Wilson p 2 1952 pores mterconnected by finecapxllary tubes and havmg Hammond fiun- Sept. 1953 abrasive articlesuniformly distributed and retained in 5 the geucdymast 2,668,153 HammondFeb. 2, 1954

1. A PROCESS FOR PRODUCING A CELLULAR ABRASIVE ARTICLE HAVING ABRASIVEPARTICLES UNIFORMLY DISTRIBUTED THEREWITHIN, WHICH COMPRISES: FORMING ANAQUEOUS SOLUTION OF POLYVINYL ALCOHOL; SEPARATELY FORMING A STABLE,AQUEOUS, FORMED MASS BY MIXING WATER WITH A SURFACE ACTIVE FORMING AGENTAND AGITATING SAME TO FORM A STABLE FOAM HAVING INDEPENDENT PORES;MIXING SAID FOAMED MASS, ABRASIVE PARTICLES AND SAID AQUEOUS SOLUTION OFPOLYVINYL ALCOHOL TO FORM A UNIFORMLY FOAMED, AQUEOUS, POLYVINYL ALCOHOLMASS HAVING ABRASIVE PARTICLES UNIORMLY DISTRIBUTED THROUGHOUT;INCORPORATING A CATALYST IN SAID FOAMED, AQUEOUS, POLYVINYL ALCOHOLMASS, AND THEREAFTER ADDING AND UNIFORMLY MIXING FORMALDEHYDE IN SAIDFOAMED, AQUEOUS, POLYVINYL ALCOHOL MASS TO REACT THE FORMALDEHYDE WITHTHE POLYVINYL ALCOHOL TO CAUSE GELATION AND RIGIDIFICATION OF SAID MASSAND THEREBY PRODUCE A CELLULAR ARTICLE HAVING INDEPENDENT PORESINTERCONNECTED BY FINE CAPILLARY TUBES AND HAVING ABRASIVE PARTICLESUNIFORMLY DISTRIBUTED AND RETAINED IN THE GELLED MASS.